The control group population in this study involves the selection of both healthy people from the medical center, there are also non-cancer populations suffering from other diseases. Therefore, the different sources of the control group is also one of the causes of heterogeneity.

This research involves the selection of the comparison group who come from both medical center's Health crowd, there are those who suffer from other diseases of the non-cancer crowd. Therefore, the control group was also different sources of heterogeneity, one of the reasons.

This research institute involves the control group crowd's selection already has comes from the physical examination center healthy crowd, also has contracts other diseases the non-cancer crowd.Therefore, control group's different origin is similarly one of reasons which the non-uniformity produces.

The Institute involves the selection of control group of people both from medical center of healthy people, there are also suffering from another disease of the cancer-free people. Therefore, control groups from different sources is also one of the causes of the heterogeneity.

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